Intangible Assets - Components of Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 343	$ 284	$ 944	$ 853
Intangible asset amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	272	225	747	665
Transition and transformation contract cost amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 71	$ 59	$ 197	$ 188